Thermostat



Patented Aug. 29, 1933 UNITED STATES PATENT OFFICE THERMOSTAT WareApplication February 14, 1931. Serial No. 515,671

6 Claims.

My invention relates to thermostats wherein the thermally movableelement is a bimetallic strip, Ordinarily, thermostats of that class areaffected by ambient temperatures and, if said movable 5 element iseither directly or indirectly connected with an electric switch, changesin the ambient temperatures effect such movement of the strip as to varythe electrical connection causing changes in resistance and sparking ifthe connection is broken. For instance, it is desirable to control anelectric motor actuating a pump in liquid dispensing apparatus embodiedin curb stands for dispensation of gasolene, by means of a thermostaticswitch which will break the circuit 15 of the pump if it is subjected toany abnormal current which might be destructive to the apparatus orignite any fumes of gasolene in the curb stand casing in which theswitch is located. The conned atmosphere in such a casing becomesabnormally hot whenever the casing is subjected to direct sunlight andin such an embodiment an ordinary bimetallic single strip thermostat isa constant source of trouble because of its move- Y ment incorrespondence with the changes in the ambient atmosphere.

Therefore, it is the purpose and effect of my invention to so constructand arrange a bimetallic thermostatic element that it is not affected byambient temperatures and therefore may be used as a switch member todirectly transmit an electric current regardless of the ambienttemperatures to which it is subjected and subject only to movementinaccordance with the heat imparted to it by the electric current.

As hereinafter described, my improved thermostatic element includes twosimilar bimetallic members disposed in opposition to each other andpreferably with heat refractory material between them serving toinsulate them from each other so that the stresses upon the assemblageincident to the ambient temperatures are counterbalanced so that thethermostatic element remains stationary as a whole despite extremeiluctuations in the ambient temperatures.

My invention includes the various novel features of construction andarrangement hereinafter more denitely specified.

In said drawing; Fig. I is a longitudinal sectional view of an electricswitch including a convenient embodiment of my invention, wherein thetwo thermostatic strip members which are opposed to each other areconnected in unitary relation by a bight at Vone end of the movableswitch member. r Fig. II is a sectional View of an electric switch,similar to Fig. I, but wherein the opposed thermo- (ci. 20o-113) staticstrip members are separate from each other.

Referring to the form of my invention shown in Fig. I, the insulatingbase 1 supports the terminals 2 and 3 of an electric circuit comprisingthe conductors 4 and 5. Said terminals 2 and 3 are normally bridged andthe circuit closed by the movable switch member '7 which is rigidlyconnected at one end with the terminal 2 and movable to and from contactwith the terminal 3 at itsopposite end.

As shown in Fig. I, said movable switch member 7 includes opposedbimetallic strip members 8 and 9 which are connected in unitary relationat one end of said member '7 by the bight 10, and said members 8 and 9are separated by the heat refractory material l1 which may be acomposition including asbestos, or any other material adapted to preventor retard the transmission of heat between said members 8 and 9. Theends of said members 8 and 9 adjacent to the terminal 70 2 areelectrically insulated from each other, conveniently by the washer 12which surrounds the screw 14, extending in threaded engagement with saidbase l and by which said thermostatic member 8 is clamped in electricalconnection with said terminal 2; said screw being electrically insulatedfrom the thermostatic member 9 by the insulating washer 15.

As indicated in Fig. I, said thermostatic members 8 and 9 each includetwo lamin, the outer one of which has a greater coefficient of expansionthan the inner one. Consequently, increment in temperature of theambient atmosphere tends to bend the thermostatic member 8 upward andthe thermostatic member 9 downward, and those stresses neutralize eachother, leaving the switch member 7 continually immovable by such changesof temperature. However, if and when the circuit 4, 5, is electricallyenergized, the member 8 forms part of the circuit but the member 9 doesnot, and, consequently, the member 8 is heated by the electric currentto a greater degree than the member 9 and bends upward carrying themember 9 with it to break the connection between the switch member 'Iand the terminal 3 and thus open the circuit whenever the temperaturefor which the device is calibrated is attained. Such calibration may beeffected by primarily bending the switch member 7 so that in theposition shown, it contacts with the terminal 3 with more or lesspressure. Of course, the greater such initial pressure of contact, thegreater increment of temperature is required to counterbalance it andeffect the oping movement of the switch. 11

The form of my invention shown in Fig. I is advantageous in that thebight 10 holds the several parts of the switch member 7 together.However, that form of thermostatic element is more costly to manufacturethan a form in which the opposed thermostatic members are formed ofdifferent pieces of bimetallic metal, as in Fig. II wherein the switchmember 17 is similar .to the switch member '7 except that the opposedthermostatic members 18 and 19 are formed of separate pieces ofbimetallic metal. of which the outer lamination of each has a greatercoefficient of expansion than the inner lamination. However, it is to beunderstood that the form of my invention shown in Fig. 1I is operativein substantially the same manner as the form of my invention shown inFig. I.

Although I prefer to interpose heat insulating material between theopposed thermostatic members, as indicated at 11 in Fig. I and at 21 inFig. II; such material may be entirely omitted from both forms of myinvention and, in the form of my invention shown in Fig. II, thethermostatic members 18 and 19 may be mechanically connected by themember 22 to transmit mechanical stresses between them induced bychanges in the ambient atmosphere.

Therefore, I do not desire to limit myself to the precise details ofconstruction and arrangement herein set forth, as it is obvious thatvarious modifications may be made therein without departing from theessential features of my invention, as defined in the appended claims.

I claim:

1. In a thermostat, the combination with opposed bimetallic members,each including two lamin of metals having diierent coemcients ofexpansion under changes of temperature; of means supporting said membersat one end thereof in spaced relation, with their lamin having the samecoefficient of expansion toward each other; and means mechanicallyconnecting the opposite ends of said members; whereby bending stressesinduced in said members by ambient temperatures counteract each otherand tend to hold said thermostat stationary, and said thermostat ismovable solely by internal changes of temperature.

2. A structure as in claim 1; wherein said members are connected inunitary relation by a bight at the end thereof remote from saidsupporting means.

3. A structure as in claim 1; wherein said members are in close parallelspaced relation, and a heat insulating material is interposed betweenthem.

4. A structure as in claim 1; wherein said members are connected inunitary relation by a bight at the end thereof remote from saidsupporting means; and heat insulating material is interposed betweensaid members and is held in said bight.

5. A structure as in claim 1; wherein the support includes means forelectrically insulating the supported ends of said members from eachother.

6. A thermostat structure as in claim 1; wherein the support includesmeans for electrically insulating the supported ends of said membersfrom each other; and an electric terminal in electrical connection withone of said members at the supported end thereof; and another electricterminal normally in separable electrical connection with the oppositeend of the member connected with said rst terminal; whereby saidstructure is responsive to changes of temperature induced in saidelectrically connected member by electric energy to bend both of saidthermostatic members out of Contact lwith the second terminal at atemperature predetermined by the construction and arrangement of saidmembers; said structure being returned to its contact relation to closethe circuit when said temperature induced by the electric current fallsbelow a predetermined degree; whereby said structure is solely movableby changes in temperature thereof independent of changes in temperatureof the ambient atmosphere.

CLARENCE E. MCGREGOR.

